Valve does not have a Linux shop for Portal 2, it is not listed as being available for Linux, there is no Announcement by Valve that it is available for Linux right now.

It would seem you read a rumor that it was finally available for Linux if you bought the Windows version (First red flag and a big one). If you bought the Windows version (not the Linux Version that is not out yet) for files that may allow some Linux Operating Systems to load the game (can't confirm myself) then you simply made a mistake by ignoring those who make the decisions and always announce this sort of news.

I'm sorry you decided to buy it before it was available. Hope it all works out later.

As for Linux coming to Valve. It was/is in beta so I would say with the files available for some and the beta it's a good bet it will definitely be coming to Linux.

The latest updates are to support MAC and Linux which many of us developers are being forced to use if we want our mods on steam while our games (indies) have the files ready. Big push by Valve to get us ready for Mac/Linux support.

Phoronix news aren't rumors. It seems there is a beta program where some limited amount of clients have access to the Linux port. I find it frustrating I can't at least join that program, it's not like there is an excessive amount of Linux gamers available.